Computer memory systems commonly include a memory controller connected to one or more memory modules via a memory channel or channels. In this context, a “memory module” is a printed-circuit board that supports and interconnects dynamic, random-access memory (DRAM) devices. Computer vendors can offer different amounts of memory by installing more or fewer memory modules, and computer users can upgrade their computers by installing different or additional modules for improved capacity or performance.
Lithographic feature size has shrunk for each generation of DRAM devices. As a result, memory systems have steadily improved in both storage capacity and signaling rates. Unfortunately, one metric of memory-system design that has not shown comparable improvement is the module capacity of a standard memory channel. That is, the number of memory modules that may be connected to a given memory channel has not grown with module capacity and speed performance.
A key reason why module capacity has not grown with other performance metrics is that each module attached to a given channel tends to degrade signals on the channel, necessitating an undesirable reduction in signal rates and concomitant reduction in speed performance. For this reason, modern memory systems are commonly limited to just one or two modules per channel when operating at the maximum signaling rate.